In the utilization of color measuring instruments, particularly reflectance instruments, having a head with an open viewing port, it is highly desirable to present samples to the instrument so that a flat distortion-free surface can be measured without compromising the repeatability and accuracy of the instrument. This goal can prove elusive when non-rigid samples (e.g. fabric samples) are being presented.
Prior art techniques for presenting non-rigid samples to a color measuring instrument are of two basic types. In the first method, the instrument viewing port is covered with an optical glass cover which protects the instrument optics from dust and lint, and allow the instrument to view a flat sample surface (essentially for repeatable results). In the second prior art method, the instrument viewing port is left open and the sample placed directly over the open port. While the color measuring instrument can be utilized according to such prior art techniques, both of these prior methods have drawbacks associated therewith.
When the first prior art method described above is utilized, there is increased heat buildup in the instrument (primarily from the light source within the instrument), and occasional distortion of the sample surface and inconsistent results due to changes in the glass cover caused by scratches, smudges, dust, and moisture. A commonly practiced solution to this problem is to utilize a heat sink to radiate excess temperature from the instrument. This heat sink is effective only at relatively low ambient air temperatures, below about 85.degree. F., and requires that the instrument be unconfined, i.e., not mounted within a desk. For speed, convenience, and safety it has become desirable for these instruments often to be mounted within a desk, thereby decreasing the effectiveness of the heat sink. Problems encountered in utilizing the second prior art method described above are the tendency of the non-rigid (e.g. fabric) samples to "bow" or "balloon" into the open viewing port, presenting a surface which is not flat, and the buildup of dust and lint (especially from fabric samples) within the instrument, adversely affecting the accuracy thereof.
According to the present invention a method and apparatus are provided that overcome most of the problems associated with prior art utilization techniques for color measuring instruments. According to the present invention it is possible to present non-rigid samples to a color measuring instrument so that a flat, distortion-free surface can be measured without compromising the repeatability and accuracy of the instrument. The invention is practiced, in its most basic terms, by providing a positive pressure of fluid (e.g. filtered air) within the instrument head, provision being provided for maintenance--but no undue buildup--of the positive pressure even when the viewing port is covered with a sample to be examined.
According to one aspect of the present invention, a method of presenting a non-rigid sample to a color measuring instrument having a head with an open viewing port is provided which comprises the following steps: Continuously supplying fluid under pressure to the instrument head to exhaust through the viewing port to prevent sample lint and dust from entering the head, to facilitate removal of heat generated by the instrument, and to facilitate maintenance of a sample so that a flat, distortion-free surface can be examined; and exhausting the fluid supply from the instrument head from a location distinct from the viewing port when the viewing port is covered with a sample to be examined. Preferably, the method comprises the further steps of disposing a backing structure in backing relationship with a non-rigid sample to be examined, and positioning the backed non-rigid sample over the viewing port with sufficient pressure to prevent the sample from moving away from the viewing port as a result of a fluid flow toward the viewing port. The fluid supplying step is preferably practiced by supplying a turbulent flow of filtered gas at a flow rate of about 10-20 cubic feet per minute through the viewing port with no sample in place, and the exhausting step is preferably practiced by providing a secondary opening having about 1/10 the effective area of the viewing port and spaced from the viewing port.
According to another aspect of the present invention there is provided a method of presenting a non-rigid sample to a color measuring instrument having a head with an open viewing port, consisting essentially of practicing the following steps substantially sequentially: Continuously supplying fluid under pressure to the instrument head to maintain the positive pressure in the head with respect to its immediate surroundings, fluid being exhausted through the open viewing port. Disposing a backing structure in backing relationship with a non-rigid sample to be examined. Positioning the backed non-rigid sample over the viewing port with sufficient pressure to prevent the sample from moving away from the viewing port as a result of fluid flowing through the viewing port; and exhausting the fluid providing a positive pressure in the instrument head from a location distinct from the viewing port when the viewing port is covered with the sample to be examined.
According to a further aspect of the present invention there is provided a method of modifying an existing color measuring instrument having a head with an open viewing port. According to this aspect of the invention a secondary opening is provided in the head having an effective area through which fluid can flow substantially smaller than the effective area of the viewing port through which fluid can flow. Then, a source of pressurized fluid is operatively connected to the head to provide fluid to the head to exhaust through the viewing port, or when the viewing port is covered, through the secondary opening, to prevent sample lint and dust from entering the head, to facilitate removal of heat generated by the instrument, and to facilitate maintenance of a sample so that a flat, distortion-free surface can be examined.
Apparatus according to the present invention comprises an instrument having a head with means defining an open port in the head over which a sample is adapted to be placed, and a source generating unwanted head located in the head (e.g. a lamp). The instrument further comprises means defining a secondary opening in the head spaced from and distinct from the port, the secondary opening being substantially smaller in effective cross-sectional area than the port; and means for providing fluid under pressure to the head and operatively connected to the head to exhaust fluid through the port, and when the port is covered, through the secondary opening. Pressure-applying means are disposed adjacent the port on the head for positioning a backed sample in place over the port without allowing movement thereof away from the port as a result of fluid flow through the port. The effective cross-sectional area of the secondary opening is about 1/10 that of the port, and the means for providing fluid under pressure is capable of delivering filtered gas under pressure to the head so that a turbulent flow of gas exhausts through the port when it is open, at a flow rate of about 10-20 cubic feet per minute.
Apparatus according to the present invention further comprises a color measuring instrument having a head with an open viewing port, and means for presenting a non-rigid sample to the instrument. The presenting means comprises means for continuously supplying fluid under pressure to the instrument head to exhaust through the viewing port to prevent sample lint and dust from entering the head, to facilitate removal of heat generated by the instrument, and to facilitate maintenance of a sample so that a flat, distortion-free surface can be examined; and means for providing exhausting of the fluid supplied to the instrument head from a location distinct from the viewing port when the viewing port is covered with a sample to be examined.
It is the primary object of the present invention to provide a simple, effective method and apparatus for presenting non-rigid samples to an instrument, particularly a color measuring instrument, so that a flat, distortion-free surface can be measured without compromising the repeatability and accuracy of the instrument. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.